(1) Field of the Invention
The present invention relates to an improved shut-off device which can be used in a single cyclone vacuum cleaner and which is preferably provided between cyclones in a dual outer and inner cyclonic vacuum cleaner. The shut-off device employs a valve means which becomes operational automatically when the outer cyclone becomes filled with dirt. The valve means shuts off the airflow between the two cyclones which prevents both fouling and damage to the motor fan unit drawing air through the cleaner and the exhausting of dirt laden air into the environment. Without the shut-off device, when the outer cyclone becomes full of dirt, additional use of the vacuum cleaner introduces dirt laden air into the inner cyclone still containing dirt particles that would have separated from the airflow had the outer cyclone been less than full. Also without the shut-off device, when the vacuum cleaner is full, additional use causes re-entrainment into the airflow entering the inner cyclone of dirt particles that had previously separated from the airflow in the outer cyclone. Therefore, the shut-off device is preferably positioned in the cleaner so as to shut off airflow to the inner cyclone when the outer cyclone becomes full of dirt.
(2) Prior Art
The prior art has described various types of devices that automatically indicate when the dirt or water level in a vacuum cleaner has reached a critical level. At that point, continued operation of the vacuum cleaner will result in ineffective or inefficient cleaning or it may cause damage to the motor fan unit. Illustrative patents are U.S. Pat. No. 2,230,113 to Hein; U.S. Pat. No. 2,758,670 to Doughman et al; U.S. Pat. No. 2,764,256 to Allen; U.S. Pat. No. 2,814,358 to Beede et al; U.S. Pat. No. 2,817,414 to Ferraris; U.S. Pat. No. 2,863,524 to Buda; U.S. Pat. No. 3,172,743 to Kowalewski; U.S. Pat. No. 3,626,545 to Sparrow; U.S. Pat. No. 3,870,486 to Eriksson et al; U.S. Pat. No. 4,246,676 to Hallsworth et al; U.S. Pat. No. 4,294,595 to Bowerman; and U.S. Pat. No. 4,623,366 to Berfield et al.
The prior art vacuum cleaner dirt level detection devices can be divided into two general categories. These devices have either floats that are designed to operate in vacuum cleaners which pick up liquids, or they have diaphragm devices that are affected by the difference in pressure between two points in the vacuum cleaner caused by the clogging of a vacuum cleaner dirt collecting bag. When the pressure differential reaches a threshold, the diaphragm triggers a sequence of mechanical or electrical steps which result in either the dust bag cover opening, a light or audible signal warning the operator to shut down the vacuum cleaner, or automatic powering down of the motor fan unit. U.S. Pat. No. 4,623,366 to Berfield et al is representative of the float type device. The float devices rely on the principle of buoyancy which causes a float to rise and seal against a seat when a sufficient amount of water has accumulated in the collection container of the vacuum cleaner. The float blocks the fan inlet opening so that even if the motor fan unit continues to run, additional water is not pulled into the system. These float devices are thus not designed to operate by sensing a differential air pressure on opposed sides of a valve. U.S. Pat. No. 2,817,414 to Ferraris is a typical vacuum cleaner employing a differential pressure diaphragm, or sensor, which detects an increase in pressure between two points in the vacuum cleaner. In this device, pressure readings are taken between the inside and the outside of a dust collecting bag. As the bag fills with dirt, a differential force is exerted upon a control diaphragm. At a predetermined threshold, the diaphragm distorts and sets in motion a sequence of pneumatic, mechanical and/or electrical steps which de-energize the motor fan unit. These latter type of control devices are both complicated and expensive to manufacture.
Cyclonic vacuum cleaners are described in my U.S. Pat. Nos. 4,373,228; 4,377,882 (Re 32257); 4,573,236; 4,593,429; 4,571,772; 4,643,748; 4,826,515; 4,853,011 and 4,853,008. There is a need for a shut-off device for these vacuum cleaners.